<!DOCTYPE HTML>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>无标题文档</title>
</head>

<body>
<form>
    请选择你爱好:<br>
    <input type="checkbox" name="hobby" id="hobby1"> 音乐
    <input type="checkbox" name="hobby" id="hobby2"> 登山
    <input type="checkbox" name="hobby" id="hobby3"> 游泳
    <input type="checkbox" name="hobby" id="hobby4"> 阅读
    <input type="checkbox" name="hobby" id="hobby5"> 打球
    <input type="checkbox" name="hobby" id="hobby6"> 跑步 <br>
    <input type="button" value="全选" onclick="checkall();">
    <input type="button" value="全不选" onclick="clearall();">
    <p>请输入您要选择爱好的序号，序号为1-6:</p>
    <input id="wb" name="wb" type="text">
    <input name="ok" type="button" value="确定" onclick="checkone();">
</form>
<script type="text/javascript">
    function checkall() {
        var hobby = document.getElementsByTagName("input");
        for (var i = 0; i < hobby.length; i++) {
            if (hobby[i].name == "hobby") {
                hobby[i].checked = true;
            }
        }

        // 任务1 :第27行处补充完整，实现当点击"全选"按钮时，将选中所有的复选项。

    }

    function clearall() {
        var hobby = document.getElementsByName("hobby");
        for (var i = 0; i < hobby.length; i++) {
            if (hobby[i].name == "hobby") {
                hobby[i].checked = false;
            }
        }

        // 任务2

    }

    function checkone() {
        var j = document.getElementById("wb").value;
        var hobby = document.getElementsByName("hobby");
        hobby[j - 1].checked = true;
        //alert(j);
        // 任务3

    }

</script>
</body>
</html>